1. Field of the Invention
The present invention relates to a shifting mechanism of the "X-Y type" for cooperation with a shift bar housing assembly for selectively shifting a change gear mechanical transmission. In particular, the present invention relates to an electrically controlled, pressurized fluid actuated X-Y shifting mechanism which is effective to cooperate with a substantially standard shift bar housing assembly of the type normally manually controlled by a shift lever allowing for the automatic or semi-automatic shifting operation of an otherwise substantially standard normally manually shifted mechanical transmission.
2. Description of the Prior Art
Shift bar housing assemblies for mechanical change gear transmissions comprising a plurality of generally parallel, independently axially movable shift bars or shift rails, each carrying a shift fork fixed thereto, and shift block mechanisms allowing a single shift bar to be selected and axially moved to effect engagement/disengagement of a particular gear ratio are well known in the prior art as may be seen by reference to U.S. Pat. Nos. 2,951,392; 4,455,883; 4,515,029; 4,567,785 and 4,584,895, the disclosures of all of which are hereby incorporated by reference.
Typically, such shift bar housings are manually controlled and operated by a shift finger fixed to a directly mounted shift lever or to the cross shaft of a remotely controlled shifting mechanism. Interlock mechanisms are usually provided to prevent movement of more than one shift rail at a time from the axially centered or neutral positions thereof.
Automatically controlled X-Y type shifting mechanisms wherein a shift finger is automatically moved in the X or rail selection direction and then in the Y or gear engagement/disengagement direction are known in the prior art as may be seen by reference to U.S. Pat. No. 2,931,237, the disclosure of which is hereby incorporated by reference.
Shift bar housing assemblies utilizing pressurized fluid actuated pistons and the like to control each shift rail in an automatic or semi-automatic mechanical transmission are known in the prior art as may be seen by reference to U.S. Pat. No. 4,445,393.
The prior art shifting mechanisms for providing automatic and/or semi-automatic shifting of mechanical change gear transmissions normally utilized with direct and/or remote manual shifting mechanisms were not totally satisfactory as substantial modification of the standard shift bar housing assembly was required, complicated valving and/or fluid/electrical connections were required, the controls were complicated and/or expensive to manufacture, assemble and/or repair, the devices did not retain the currently engaged gear in engagement if the electrical/pressurized fluid sources were interrupted, and/or the controls did not provide a rapidly and positively obtainable neutral position and a reliable indication device therefor.